well, i still think the best way is to walk around looting buckets and goblin mails xD, oh oh, another good one- sell chickens xD.
A good way would be to get skills to high levels and then gaining items sell them. there are 3 big ones (skills) woodcutting, favored by many players. start with normal trees, at 15 move to oaks, from 35-40 move to willows until lvl 70 to cut yews for money. (70 so they would go fast, as at 60 it takes ages, of course, u can start cutting them when u want), and sell yews 300 ea.
fishing- start with low level fishes (also increasing ur cooking), until lvl 45. fish lobsters (again , 45 cause of being faster, but u can start at 40). cook them, and sell up to 300ea.
Mining- go to 15 with coppers and tins, from 15 mine to 45. start on coal, but it will go slow, although its quite good money. after getting some money from coal (170ea), use iron (cause at ¬50 mining itll only take 1 hit) to get to about 70. start mining mithril- 400ea. then adamant at about 80-85, (1-2kea). finally, you can start minin' rune (12-15kea!) at about lvl 90. there are only 3 rune rocks for free world- in lvl 40 wilderness, and they respawn slowly, so mine in the mornings and switch servers. other skills like crafting, can help you mae ur own items from, e.g. cowhides for pure profit. cowhides- god idea aswell, 100ea. rune essence- 20-30ea. if ur high lvl combat just kill lesser demons and wait for rune items to drop.
every skill in the game can bring rewards- so use them and itll be easy ;)

I have found this question many times on this forum and my answer is train a skill to your satisfaction and just go witht he skill to make money its alot easier and it will never dissapear infact it will only get better as more opppurtunities will open with your skill.